1. Field Of The Invention
The underdrain of the present invention is designed generally for usage with filtering chambers useful for the filtering and cleaning of liquids, particularly water, by passage of the liquid through a bed of filtering media usually granular as used in swimming pool filters and the like. In most designs the filtering chamber is formed by a filter tank which is partitioned into an upper section which contains the filtering media and a lower section from which the cleaned fluid is returned. These sections are partitioned or separated from one another by the underdrain. The liquid to be cleansed is supplied to the top of the filtering media and passes downwardly by the force of gravity and/or by pumping through the filtering media which cleans the liquid. The liquid then passes through the perforated underdrain into the lower section. The holes or apertures within the underdrain must be small enough to prevent the passage of the particularly chosen filtering media but large enough to admit freely the passage of the liquid therethrough.
Such filtering systems must also provide a means for cleaning of the filtering media without withdrawing the filtering media from the filter tank. The usual process is a backwashing of a cleaning liquid through the filtering system in the reverse direction with respect to the normal direction of flow for filtering.
2. Description Of The Prior Art
One example of an underdrain configuration useful with the filtering devices of the present field of art is U.S. Pat. No. 3,519,135 issued July 7, 1970. In this patent a perforated underdrain is utilized in which the apertures within the underdrain plate are chosen with a vertically extending pronged structure such that during backwashing the fluid is directed upwardly in a jetting action to aid in the freeing of dirt and other substances which have been accumulated during the immediately previous period of filtering operation. Other U.S. patents showing similar construction for particulate material filtering include U.S. Pat. Nos. 3,142,642 and 3,625,365. These designs include various pipes, arms and apertured devices for providing full filtering of the liquid while still providing a convenient means of backwashing the filter tank.
The present apparatus provides a unique design which overcomes many of the problems of the prior art since the backwashing water is directed outwardly toward the walls of the filter tank by the novel configuration of the slots within the filter underdrain. This advantage and further advantages of the present invention will be apparent from a review of the disclosure.